This study aimed to identify a suitable non-pathogenic surrogate for industrial validation of the irradiation process by high energy electron beam (5 MeV) of dried seeds. Pumpkin seeds and flax seeds were contaminated with a five-strain Salmonella cocktail comprising five different serovars or a two-strain Escherichia coli cocktail comprising pathogenic strains, including E. coli O157:H7. Comparison of log survival fractions of the E. coli and Salmonella cocktails revealed that on both seeds the Salmonella cocktail exhibited higher tolerance against high energy electron beam at doses of 4 kGy than the E. coli cocktail. For surrogate selection, the Salmonella cocktail, and the strains E. coli DSM 18039 (strain MG1655) and Enterococcus faecium NCCB 86023 (strain NRRL B-2354) were subjected to electron beam processing of doses of 2 to 6 kGy. The calculated D 10 -values of the Salmonella cocktail were rather similar to that of E. coli DSM 18039, i.e. 1.07 kGy compared to 1.20 kGy on pumpkin seeds and 0.88 kGy compared to 1.07 kGy on flax seeds. E. faecium NCCB 86023 exhibited three times higher tolerance on pumpkin seeds (3.07 kGy) and two times higher on flax seeds (2.22 kGy), compared to the Salmonella cocktail. Hence, the apathogenic E. coli DSM 18039 was suggested to serve as surrogate for Salmonella in industrial validation trials. As on both seeds E. faecium NCCB 86023 showed higher tolerance against electron beam than the Salmonella cocktail, this apathogenic strain could serve as an indicator strain for the efficacy of decontamination of dried seeds by electron beam.

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